The Collaborative International Dictionary of English v.0.48:

Amphistylic \Am`phi*sty"lic\, a. [Gr. ? + ? pillar, support.]
   (Anat.)
   Having the mandibular arch articulated with the hyoid arch
   and the cranium, as in the cestraciont sharks; -- said of a
   skull.
   [1913 Webster] Amphitheater